I have been trying to book an Aer Lingus flight ex Dublin and the system keeps coming back saying that 'there are no seats available within 14 days either side of the required dates', seems mad, I thought at first that the route was n/a and then tried DUB LHR but the same message. Mad!!
EI-BUD
Often happens when the system has been re-configured or the fare base has been altered. For example, promotional and I must say proactive Business Class fares with a €200 rountrip discount were loaded overnight and are available from this morning. Tweaks like this with the system can often lead to an error or intermittent glitch developing. I've seen the above mentioned error several times on the Aer Lingus website.
Also try closing out of the Aer Lingus website and clearing your browser before logging back on again, that is sometimes the issue if you have carried out multiple flight searches.
EI Premier